#1579 Enforce ordering in SourceList.cmake
The script generate_cmake_source_list.py generates automatically the list of subdirectories using os.walk, which proceeds in an arbitrary order...
So re-running the script could result in many trifle changes because the ordering is not the same (empirically I saw that it didn't change for a given version of Python but could change when run with a newer Python later on).
So I have just added a sort to enforce alphanumerical ordering, thus limiting the issue.